1. Field of the Invention
The present invention relates in general to a grating-coupled waveguide and, in particular, to a grating-coupled waveguide that includes a substrate, a diffraction grating and a waveguide film that has a higher index of refraction than the substrate which has an index of refraction≦1.5.
2. Description of Related Art
Grating-coupled waveguides (GCWs) can provide a very narrow spectral response to incident light emitted from an optical interrogation system, and have therefore been used in a wide variety of applications including optical filters, laser cavity mirrors and biosensors (for example). In the biosensing application, the optical interrogation system monitors variations in the optical response of the GCW as a biological substance is brought into contact with the GCW, thereby altering the monitored optical response of the GCW through material binding, adsorption etc. . . . In this manner, the GCW enables direct optical monitoring of biological events, allowing label-free assays where the expense and experimental perturbations of fluorescent dyes are completely avoided. In order to produce competing functionality however, GCWs need to be optimized in terms of sensitivity to detect biological substances. The present invention relates to a design modification of a traditional GCW that enables one to make and use a highly sensitive GCW.